The present invention relates to a wheel for motor vehicles and a method of manufacturing such a wheel.
Wheels for motor vehicles are generally formed of two pieces of steel, namely the disk and the rim, made by the pressing or forming of profiled members which are then assembled by welding. The use of steel makes it possible to obtain very good mechanical and thermal performance in the manufacture of heavy wheels. With the emphasis placed today on the saving of energy, one major concern of automobile manufacturers is to reduce the weight of the parts of the automobile, such as the wheels, in order to decrease the consumption of gasoline and improve the maneuverability of the vehicles.
One solution consists in making the wheels of light alloys; however, their cost price is three to five times greater than that of steel wheels. The use of plastics is another solution which makes it possible to effect a large reduction in weight, but it is difficult to obtain sufficient mechanical properties in the wheels obtained and furthermore problems arise with respect to the removal of the thermal energy transmitted by the brake disks.
For this reason, other solutions have been developed, such as so-called "hybrid" wheels which have a metal disk, which assures both the properties of resistance and thermal conduction, and a plastic rim, which permits a saving in weight.
Thus, WO 93/01946 describes a wheel which comprises an essentially metallic disk and a plastic rim, which are manufactured separately and then assembled by screwing. However, the assembling by screwing results in a high cost of industrialization and requires very great precision in order to obtain good coaxiality between the disk and the rim.
Furthermore, the presence of screw support elements at certain points of the wheel creates fragile zones which present further risks of rupture. Finally, the screwing on of a plastic material causes a flow of the material in the screwing region and hence a change, over the course of time, in the initial clamping produced and therefore a joint-disk connection which is not reliable. Moreover, this connection is greatly stressed under the effect of the inflation pressure of the tire and the external constraints experienced during travel.
JP-A-03193501 shows a different embodiment of a hybrid wheel formed by a metal disk of light alloy and by a rim comprising a first inner part of light alloy in contact with the disk and a second outer part of plastic bonded to the first part of the rim. This construction involves combining the metal disk and the first metal part of the rim by molding or forging, and then of finishing this first part by mechanical processes in order to produce therein a circumferential groove and holes which together form protrusions on the circumference of said first part of the rim, and finally of a molding of the second plastic part of the rim on the first part in such a manner that the second plastic part rests on the end of the outer surface of the first part and covers the protrusions. The connection between the two parts of the rim, effected by the resting of the second part on the first, is thus reinforced by a unity in rotation obtained by the presence of the covered protrusions.
This wheel, due to this additional rim inner part, is of a complicated structure. On the one hand, the presence of this additional inner part of light alloy increases the cost of manufacture of such a wheel, due to the sensitivity of the cost to the amount of expensive light alloy used and, on the other hand, due to the numerous manufacturing steps which it requires and which increase the time of manufacture of the wheel. Furthermore, the resting obtained between the two parts of the wheel constitutes a connecting zone of poor tightness.